Method for controlling a super-charged internal combustion engine

ABSTRACT

A control method for a supercharged internal combustion engine wherein actual supercharging pressure values are adjusted to prescribed desired supercharging pressure values by setting a variable component and influencing the supercharging pressure of a supercharger in accordance with a prescribed control law. In order to monitor the control of supercharging pressure in a supercharged internal combustion engine with the aid of simple means and, if appropriate, to display a malfunction, use is made as control law of a PID controller, the integration component is compared in the integration element of the PID controller with a prescribed tolerance band, and a fault signal is generated if the integration component is outside the tolerance band.

BACKGROUND AND SUMMARY OF INVENTION

This application claims the priority of 198 44 212.2, filed in Germanyon Sep. 26, 1998, and PCT/EP99/06342 filed in Europe on Aug. 28, 1999,the disclosures of which are expressly incorporated by reference herein.

The invention relates to a control method for a supercharged internalcombustion engine.

German Reference DE 40 25 901 C1 discloses an exhaust gas turbochargerfor an internal combustion engine which has a turbine with a turbinegeometry which can be variably set via a variable turbine guide vane,and a compressor, driven by the turbine, for raising the superchargingpressure in the cylinder inlet. The turbine guide vane can be adjustedwith the aid of an actuator so as to vary the active cross section ofthe turbine. It is possible therefore, depending on the operating stateof the internal combustion engine, to implement exhaust back pressuresat various levels in the section between the cylinders and the exhaustgas turbocharger, as a result of which the output of the turbine and thepower of the compressor can be adjusted depending on need. The turbineguide vane is controlled to a desired supercharging pressure inaccordance with prescribed characteristic lines.

In order to achieve an improvement in efficiency with simple means in anon-stationary operation of the internal combustion engine, thesupercharging pressure is controlled below and above a threshold valuefor the exhaust back pressure in accordance with differentcharacteristic lines. It is possible thereby to prevent the occurrenceof uncontrolled pressure rises in the exhaust pipe upstream of theturbine after a positive load change during the rise in superchargingpressure. The internal combustion engine need no longer emit against araised exhaust back pressure, and the efficiency is raised.

The supercharging pressure of such internal combustion engines isfrequently adjusted to the desired value with the aid of a superchargingpressure controller implemented as a PID controller, the superchargingpressure controller applying the required control signal to anadjustable supercharger component influencing the superchargingpressure. Since the supercharging pressure substantially influences thevehicle operation in the activated drive operating mode and, inparticular in the case of heavy commercial vehicles, also in enginebraking operation, the functionality of the controller and/or of thecomponents participating in the control must be regularly checked.

The invention is based on the problem of monitoring the control ofsupercharging pressure in a supercharged internal combustion engine withthe aid of simple means and, if appropriate, displaying a malfunction.

The novel control method uses a PID controller for adjusting the desiredsupercharging pressure. The integration component of the PID integrationelement usually increases continuously with time. According to theinvention, this integration component is now compared with a toleranceband which is prescribed with a tolerance value at either end as anideal integrator mean value. If the integration component exceeds orfalls below the tolerance band, a defective operating state is present,and a fault signal is produced to assist in the identification of thedefective state during the controlling of the supercharged internalcombustion engine. This defective state can be classified as a fault oflow severity as long as only the integration component is outside thetolerance band, but otherwise the system deviation of the integrationelement is still approximately zero, which means the PID controller isstill capable of controlling to the prescribed desired superchargingpressure value.

This method has the advantage that faults can be identified clearly andreliably in running operation without additional measures such as, forexample, workshop interventions with additional test procedures.

In a particularly advantageous way, the method includes the use of a PIDcontroller and a system deviation is detected by comparison with a limitvalue and used to generate a fault signal. This defective state can beclassified as a severe fault, since a remaining system deviation whichis not allowed to occur with the use of an integration element in thecase of a correct mode of operation renders it impossible to set thedesired supercharging pressure.

The combination of monitoring the integration error and the systemdeviation represents a complete safety concept which manages withoutadditional outlay on hardware, such as sensors or the like, and can beimplemented with a low outlay. In this case, the monitoring can beperformed in two stages, firstly by checking the integration componentin a first stage, and in a second stage also checking the systemdeviation for the case when the integration component is outside thepermitted range.

In the case of a fault, a fault signal is generated and expedientlyinput into the engine regulation and control system of the internalcombustion engine. Both in the case of a fault in the first stage and inthe case of a fault in the second stage, a fault signal is generated ineach case, it advantageously being possible to differentiate the type offault via specific markings of the fault signals.

The derivative-action element of the PID controller can be set to zeroif appropriate. The controller reduces to a PI controller in this case.

The control method is preferably used in combination with an exhaust gasturbine with variable turbine geometry which can be used to control thesupercharging pressure by adjusting the variable control device of theturbine geometry in accordance with prescribed supercharging pressurecharacteristic diagrams up to the setting of the desired superchargingpressure.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and expedient embodiments are to be gathered from thefurther claims, the description of the figures and the drawings, inwhich:

FIG. 1 shows a diagrammatic view of a supercharged internal combustionengine with supercharging pressure control,

FIG. 2 shows a block diagram of a supercharging pressure controller, and

FIG. 3 shows a flowchart for checking faults.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The internal combustion engine 1 in a motor vehicle, for example adiesel internal combustion engine in a commercial vehicle, has anexhaust gas turbocharger 2 with a compressor 3 in the induction tract 4,and an exhaust gas turbine 5 in the exhaust line 6. The compressor 3,which produces a raised supercharging pressure at the cylinder inlet ofthe internal combustion engine 1, is connected via a shaft to theturbine 5, which is driven by the exhaust gas flow of the internalcombustion engine.

The turbine 5 is fitted with a variable, adjustable turbine geometry,which is designed in the exemplary embodiment as a radial guide cascade7 with adjustable guide vanes and is set by an actuator 8 to the desiredguide cascade position. As an alternative to a radial guide cascade, thevariable turbine geometry can also be implemented as an axial slide. Useis also made, if appropriate, of flap turbines or other types ofvariable turbine which permit variable adjustment of the active turbinecross section or, in some other way, permit the exhaust mass flowstriking the turbine impeller to be influenced.

The vehicle is subordinate to an engine regulation and control system 9for regulating and controlling the driving and operating states of theinternal combustion engine 1, the exhaust gas turbocharger 2 and, ifappropriate, further components such as gearbox etc. The engineregulation and control system 9 communicates with various enginecomponents via signal lines 10 to 14. Via the signal lines 10, 11, theengine regulation and control system 9 receives engine state variablesand engine operating variables as input signals, in particular theengine load M_(L) and the engine speed n. In accordance with a storedtransformation rule, for example a control law, and as a function ofstored characteristic diagrams, the engine regulation and control system9 generates from the input signals output signals which are fed to theengine components to be set via further signal lines 12, 13, 14. Theengine regulation and control system 9 controls the mode of operation ofthe injection nozzles 15 and of the valves 16 of the internal combustionengine 1 via the signal lines 12, 13. The actuator 8 is fed via thesignal line 14 a control pressure P_(D) which is converted in theactuator 8 into an actuating travel s for setting the variable turbinegeometry.

The control system of the exhaust gas turbocharger 2 is illustrated inthe block diagram in accordance with FIG. 2. The engine control andregulation system 9 comprises a characteristic diagram 17 and a PIDcontroller 18 which is composed additively of the individual componentsof proportional element 19, integral element 20 and derivative-actionelement 21. The engine control and regulation system 9 is fed as inputsignals the engine load M_(L) and the engine speed n, from which thedesired supercharging pressure p_(2S,desired) for the induction tract ofthe internal combustion engine downstream of the compressor is read outin the characteristic diagram 17. The system deviation Δp_(2S), which isfed as input signal to the PID controller 18, is formed from the desiredsupercharging pressure p_(2S,desired) by subtracting the measured actualsupercharging pressure value p_(2S,actual). In accordance with thecontrol law

S _(St) =S _(P) +S _(I) +S _(D)

the PID controller supplies the pulse-width-modulated actuating signalS_(St), comprising the components S_(P), S_(I) and S_(D) which areassigned to the individual elements 19, 20, 21 of the controller and aredetermined from the components of the PID controller in accordance withthe relationships

S _(P) =K _(P) *Δp _(2S)

S _(I) =K _(I) *p _(2S) ^(dt)

S _(D) =K _(D) *d/dt(Δp _(2S))

Here, K_(P), K_(I) and K_(D) denote gains of the proportional element19, the integral element 20 and the deviate-action element 21,respectively.

The actuating signal S_(St) is fed as input signal to a transducer 22 inwhich a control pressure P_(D) is generated as output signal.

It can be expedient to subordinate the transducer 22 to a controllerG_(R), in order to compensate fluctuations in the pressure supply sothat pressure fluctuations cannot affect the control pressure p_(D)generated.

The control pressure P_(D) is fed as input signal to the actuator 8,which generates the actuating travel s for the variable turbine geometryin the exhaust gas turbocharger 2 of the internal combustion engine 1.

The integration element 20 of the PID controller 18 is assigned a faultblock 23, in which continuous checking of the operating state of theinternal combustion engine is undertaken with the aid of the integrationcomponent S_(I) of the PID controller, and with the aid of the systemdeviation Dp_(2S), and any faults occurring are recorded. The design andmode of operation of the fault block 23 is illustrated in detail in FIG.3.

In accordance with FIG. 3, the fault block 23 comprises a plurality ofprocessing and memory units 24 to 26. In a first processing unit 24, acheck is made as to whether the integration component S_(I) generated inthe integration element 20 is within a tolerance band which is boundedby a lower, prescribable tolerance value Tol_(min) and an upper,prescribable tolerance value Tol_(max).

If the integration component S_(I) is within the tolerance band, nodefective operating state is present. In accordance with a first design,the fault checking can be broken off and the closed-loop control can becontinued. In accordance with a second design, the fault checking canalso be continued for the case in the downstream processing unit 25 whenthe integration component S_(I) is within the prescribed tolerance band.

If the integration component S_(I) is outside the tolerance band, adefective operating state is present. The fault is documented in amemory unit 26 by inputting the integration component S_(I) and thecurrent point in time, and also displayed, if appropriate.

In the case of a fault, it is expedient to continue the checking in thedownstream processing unit 25, in which it is asked whether the systemdeviation Δp_(2S), which must vanish when use is made of an integrationelement, is smaller than a given limit value P_(limit). No fault ispresent if this is the case. By contrast, if the system deviationΔp_(2S) is larger than the limit value P_(limit), the controller is notcapable of adjusting the supercharging pressure to the prescribeddesired supercharging pressure, and a lasting system deviation ispresent. Dynamic transient phenomena are to be taken into account inthis case, since a lasting system deviation can be detected withadequate reliability only in the stationary operating state. In order tobe able to exclude non-stationary processes, it is expedient toinvestigate the system deviation Dp_(2S) in a plurality of consecutivecycles.

In the case of an impermissibly high system deviation, a fault is inputinto the memory unit 26.

It can be appropriate to undertake the fault checking in the twoprocessing units 24 and 25 in a fashion independent of one another ineach case.

It can also be appropriate to use a PI controller instead of a PIDcontroller. This is achieved by setting the gain K_(D) of thederivative-action element 21 to zero.

The integration component S_(I) is expediently represented as anintegrator sum which can be determined by numerical iteration, and istaken as the basis for the comparison with the tolerance band. Since theintegrator sum increases continuously with time, the tolerance band mustbe updated continuously in accordance with the current point in time.

What is claimed is:
 1. A control method for a supercharged internalcombustion engine, in which actual supercharging pressure values(p_(2S,actual)) are adjusted to prescribe desired supercharging pressurevalues (p_(2S,desired)) by setting a variable component, influencing thesupercharging pressure of a supercharger in accordance with a prescribedcontrol law, comprising the steps of: using a PID controller having anintegration component, a proportional component and a derivativecomponent, said PID controller functioning as said prescribed controllaw, and comparing said integration component with a prescribedtolerance band (Tol_(min), Tol_(max)); and generating a fault signal ifthe integration component is outside the tolerance band (Tol_(min),Tol_(max)).
 2. The control method according to claim 1 furthercomprising the steps of: forming a system deviation (Δp_(2S)) betweenthe desired supercharging pressure value (p_(2S,desired)) and the actualsupercharging pressure value (P_(2S,actual)); and generating a faultsignal if the system deviation (Δp_(2S)) exceeds a defined limit value(p_(limit)).
 3. The control method according to claim 2 furtherincluding the step of monitoring the integration component (S_(I)) andthe system deviation (Δp_(2S)).
 4. The control method according to claim2 including the steps of representing the integration component (S_(I))approximately as an integrator sum, and comparing the integrator sumwith the tolerance band (Tol_(min), Tol_(max)).
 5. The control methodaccording to claim 2 including the step of storing a generated faultsignal in a engine regulation and control system.
 6. The control methodaccording to claim 2 including the step of controlling the superchargingpressure as a function of a load (M_(L)) and engine speed (n).
 7. Thecontrol method according to claim 2 including the step of setting thederivative component element of the PID controller to zero.
 8. Thecontrol method according to claim 1 further including the step ofmonitoring the integration component (S_(I)) and the system deviation(Δp_(2S)).
 9. The control method according to claim 8 including thesteps of representing the integration component (S_(I)) approximately asan integrator sum, and comparing the integrator sum with the toleranceband (Tol_(min), Tol_(max)).
 10. The control method according to claim 8including the step of storing a generated fault signal in a engineregulation and control system.
 11. The control method according to claim8 including the step of controlling the supercharging pressure as afunction of a load (M_(L)) and engine speed (n).
 12. The control methodaccording to claim 8 including the step of setting the derivativecomponent element of the PID controller to zero.
 13. The control methodaccording to claim 1 including the steps of representing the integrationcomponent (S_(I)) approximately as an integrator sum, and comparing theintegrator sum with the tolerance band (Tol_(min), Tol_(max)).
 14. Thecontrol method according to claim 13 including the step of storing agenerated fault signal in a engine regulation and control system. 15.The control method according to claim 13 including the step ofcontrolling the supercharging pressure as a function of a load (M_(L))and engine speed (n).
 16. The control method according to claim 1including the step of storing a generated fault signal in a engineregulation and control system.
 17. The control method according to claim16 including the step of controlling the supercharging pressure as afunction of a load (M_(L)) and engine speed (n).
 18. The control methodaccording to claim 1 including the step of controlling the superchargingpressure as a function of a load (M_(L)) and engine speed (n).
 19. Thecontrol method according to claim 1 including the step of setting thederivative component element of the PID controller to zero.
 20. Thecontrol method according to claim 1 wherein the supercharger is anexhaust gas turbocharger with a compressor and an exhaust gas turbinehaving a variable turbine geometry, and wherein the actual superchargingpressure values (P_(2S,actual)) are adjusted to the desiredsupercharging pressure values (P_(2S,desired)) by setting the variableturbine geometry.